The present invention relates, in general, to apparatus and methods for protecting a catalytic converter from engine misfires in a multi-cylinder internal combustion engine.
Modem spark ignition engines utilize an engine control computer or ECC. Outputs to the engine from the ECC include signals that control the electric spark to each individual cylinder. Individual signals are also provided to control the opening and closing of the individual cylinder fuel injectors.
The ECC receives information from various engine sensors. Typically, the sensors provide information on inlet mass air flow, throttle position, intake manifold pressure, crankshaft position, engine coolant temperature and exhaust oxygen content. A typical crankshaft position sensor might include a sensing device, either magnetic, optical, Hall effect, etc., which detects the presence of a series of teeth or marks on the engine crankshaft. A tooth in this configuration may be uniquely designed to provide a reference point such that the identification of a particular cylinder is indexed to the reference point.
A large number of engines are also equipped with an exhaust oxygen sensor. The sensor is necessary for the precise control of the air to fuel ratio (A/F) of the engine. Typically, the exhaust oxygen sensor outputs a high signal when the exhaust A/F ratio is rich of a stoichiometric value. When the exhaust A/F is lean of stoichiometry, the sensor output is low. The oxygen sensor is typically used in a closed loop fuel control arrangement which has both short term and long term learn corrections. This precisely regulates the engine A/F ratio to a stoichiometric value. An engine exhaust catalytic converter, which is used to promote full oxidation of hydrocarbons, carbon monoxide, and reduction of nitrogen oxides present in the engine exhaust gases, operates very efficiently at a stoichiometric exhaust A/F ratio.
It has been previously found that a catalytic converter may be damaged if engine cylinder misfire occurs. The source of such misfires could be a disconnected or broken spark plug wire or a wire to a fuel injector. Other engine problems can result in the lack of or incomplete combustion of a particular cylinder which is also referred to as a misfire.
Typically, when cylinder misfire occurs, the unburned fuel that is discharged into the exhaust passage from the misfiring cylinder greatly increases the reaction temperature of the converter to an extent that may lead to overheating of the converter.
The vehicle manufacturers provide alarms, such as a flashing light, to alert the vehicle driver when damaging engine misfire occurs above a threshold level. Information from the crankshaft position sensor is commonly used to detect engine misfire. The speed variation of the crankshaft is measured about the combustion event of each cylinder. Speed variations are compared to known operating characteristics to deduce when a misfire occurs. An abnormal crankshaft speed variation at the expected power stroke may be counted as a misfire for a specific cylinder. A number of misfires may be counted for a certain amount of time, i.e., five seconds, which defines a known as xe2x80x9ccylinder misfire counterxe2x80x9d. this type of misfire detector can experience certain difficulties accurately detecting engine cylinder misfire. Frequency related torsional resonance of the crankshaft may give a false signal at certain operating RPMs. Driveline induced speed fluctuations to the crankshaft may also occur when the vehicle is operated on a rough road surface.
It would also be desirable to provide a method and apparatus which is capable of taking corrective action to protect the engine catalytic converter in the event of an engine cylinder misfire. It would also be desirable to provide a method and apparatus which is capable of preventing the removal of engine power when no engine misfire exists.
The present invention is a method and apparatus for protecting an engine converter during misfire in at least one cylinder of a multi-cylinder internal combustion engine.
The method controls engine parameters during an engine cylinder misfire in at least one cylinder of a multi-cylinder internal combustion engine. The method comprises the steps of:
detecting a cylinder misfire in at least one cylinder of a multi-cylinder engine;
counting the number of misfires in each cylinder on a cylinder by cylinder basis;
integrating the misfire count for each positive change of the misfire count for each cylinder over time;
establishing a first threshold based on the integrated misfire count;
establishing a second threshold for a short term fuel control signal adjusting the flow of fuel to each cylinder of the engine;
comparing the integrated misfire count and the short term control signal with the first and second thresholds; and
if the first and second thresholds are exceeded at substantially the same time, shutting off fuel to at least one cylinder of the engine in which the misfire is occurring and shutting off the short and long term fuel control.
The method of the present invention optionally includes a verification sequence including the steps of:
upon the occurrence of a detected misfire, determining in a first determination the engine cylinder numbers in which the fuel is shutoff;
in a second determination repeating all of the method to determine the cylinder number of cylinders in which fuel is shut off;
comparing the cylinder numbers from the first determination with the cylinder numbers from the second determination to determine a match;
if the cylinder numbers in the first and second determinations match, ending misfire detection control; and
if the cylinder numbers in the first and second determinations do not match, turning on fuel to all of the cylinders and resetting the misfire counter to a reset value.
The apparatus of the present invention includes means for receiving an output signal indicative of the occurrence of a misfire in at least one cylinder of a multi-cylinder internal combustion engine. A counter counts the number of misfires in each cylinder of the engine on a cylinder by cylinder basis. Means are provided for integrating the misfire counter positive changes over time. Means are also provided for comparing the integrated misfire counter output with a first threshold. Means are provided for comparing a fuel short term correction signal with a second threshold. Means are provided for determining when the integrated misfire counter output exceeds the first threshold at substantially the same time that the fuel short term correction signal exceeds the second threshold. The determining means provides an output signal for corrective engine control which is used by an engine controller to shut off the fuel to the engine cylinders in which misfire is occurring, and shut off the short and long term fuel correction.
Means are optionally provided for verifying that the fuel has been shut off to the proper cylinders in which misfire was occurring. The verification means or sequence includes means for redetermining the number of cylinders in which fuel is to be shut off due to the occurrence of misfire and in comparing the number of cylinders in which fuel has been shut off by a first execution of the control method with the number of cylinders in which fuel is to be shut off from a second execution or determination by the control method.
If the cylinder numbers match in the two determinations, engine misfire control is terminated. However, if the engine cylinder numbers do not match, fuel is turned on to all of the engine cylinders and the various perimeters in the control method and apparatus of the present invention are reset to nominal values for the restart of the sequence of the present invention.
The engine converter misfire protection method and apparatus of the present invention uniquely determines when damaging cylinder misfire is occurring, which cylinder of the engine in which the misfire is occurring and takes corrective action by shutting off the flow of fuel to the misfiring cylinder and shutting off the short and long term fuel correction. This prevents the output of the engine oxygen sensor from switching to a state which previously resulted in the application of additional fuel to the engine cylinders. The present control method and apparatus protects the converter and maintains the temperatures within the various portions of the converter at essentially nominal operating temperatures despite the occurrence of cylinder misfires.